A 6-year-old, 29-kg (63.8-lb) castrated male Australian Shepherd was referred to a veterinary specialty hospital for evaluation of hypoglycemia. At the initial visit, results of a physical examination were unremarkable. The dog had a 2-week history of progressive exercise intolerance, lethargy, and polydipsia. Hematologic testing performed 4 days prior to the referral examination revealed substantial hypoglycemia (BG concentration, 38 mg/dL; reference range, 63 to 114 mg/dL). Subsequent evaluation by the referring veterinarian revealed persistent postprandial hypoglycemia despite repeated feedings. At 11 am, the dog's BG concentration was 54 mg/dL and it was fed, followed by another BG measurement at 12:30 pm (41 mg/dL). At 2:30 pm, the dog's BG measurement was 50 mg/dL, and it was fed again; at 4:30 pm, the BG measurement was 47 mg/dL.
Additional diagnostic evaluations, including abdominal ultrasonography, urinalysis, thoracic radiography, and an ACTH stimulation test were performed at the referral facility, and venous blood samples were collected for endogenous plasma ACTH concentration measurement and assessment of the serum insulin-to-glucose concentration ratio. The ultrasonographic examination revealed mild hepatomegaly, but no lesions were detected that would affect the pancreas. Results of urinalysis and the radiographic examination were unremarkable. The ACTH stimulation test was performed by collecting a venous blood sample immediately before (baseline) and 1 hour after administration of cosyntropina (5 μg/kg [2.3 μg/lb], IV). Collected serum was sent to a commercial laboratoryb for measurement of cortisol concentrations. The pre-ACTH stimulation and post-ACTH stimulation cortisol concentrations were < 0.5 and 3.2 μg/dL, respectively. The reference rangesb for pre-ACTH and post-ACTH stimulation cortisol concentrations in healthy dogs were 2 to 6 and 6 to 18 μg/dL, respectively, with post-ACTH stimulation values of 18 to 22 μg/dL considered equivocal and post-ACTH stimulation values > 22 μg/dL considered consistent with hyperadrenocorticism. Blood was collected in an EDTA-containing tube after food was withheld for 12 hours, and the sample was submitted for measurement of endogenous plasma ACTH concentration.b The result (< 5 pg/mL, with testing performed in duplicate and verified by repeat analysis) was interpreted to be inconsistent with primary hypoadrenocorticism. Analysis of SG and serum insulin concentrationsb in the unfed patient revealed hypoglycemia (SG concentration, 59 mg/dL) and a circulating insulin concentration of 34.8 μU/mL (reference range, 5.2 to 41.5 μU/mL). The serum insulin-to-glucose concentration ratio was high (77; reference range, 14 to 43).
An insulinoma was suspected on the basis of persistent hypoglycemia and the high serum insulin-to-glucose concentration ratio. Medical treatment was initiated with prednisonec (0.7 mg/kg [0.3 mg/lb], PO, q 12 h) as a means of potentially increasing insulin resistance, reducing glucose metabolism, increasing hepatic glucose production, and impairing insulin secretion. In addition, exploratory abdominal surgery and potentially a partial pancreatectomy were recommended. With the patient under general anesthesia, a laparotomy was performed, and intraoperative examination revealed that the pancreas was normal in appearance with no masses or enlarged lymph nodes. A partial left pancreatectomy was performed, 1 lymph node near the celiac artery was excised, and a biopsy sample was obtained from the left medial lobe of the liver with a guillotine technique. The patient recovered from the procedure without complications, and BG concentrations remained stable (> 60 mg/dL) during the postoperative period. The patient was discharged from the hospital with tramadold (3.4 mg/kg [1.5 mg/lb], PO, q 8 h), a tapering dose of prednisonec to be discontinued approximately 1.5 months after surgery, and a plant-based homeopathic preparatione (10.3 mg/kg [4.7 mg/lb], PO, q 12 h).
The liver biopsy, regional lymph node, and pancreas samples were submitted to a commercial reference laboratory for histologic examination and histochemical staining by one of the authors (MDC). The tissue sections were fixed in neutral-buffered 10% formalin solution, routinely processed (ie, embedded in paraffin wax and sectioned at 5 μm), and stained with H&E. Immunohistochemical staining was performed on sections of pancreas with a peroxidase-based polymer system.f Primary (IgG) antibodiesg included polyclonal guinea pig anti–swine insulin, polyclonal rabbit anti–human glucagon, polyclonal rabbit anti–rat somatostatin, monoclonal mouse anti–human pancytokeratin (clone AE1-AE3), and monoclonal mouse anti–human cytokeratin 7; all were cross-reactive with the respective canine proteins. Secondary antibodiesg were matched to the primary antibody host. Positive reactions were visualized with the chromogen 3-amino-9-ethylcarbazole, and sections were counterstained with Mayer hematoxylin. Serial sectioning of the pancreas sample did not reveal any discrete masses or lesions. Microscopic examination of the pancreas revealed numerous enlarged islets that were haphazardly and randomly arranged throughout the parenchyma. The islets subjectively appeared to be increased in size. Constituent islet cells were increased in number, and some were slightly hypertrophied. Cellular and nuclear atypia and mitotic activity were absent (Figure 1). Ductuloinsular complexes, comprising endocrine islets in intimate association with small-sized ducts, were present in low numbers. There were no overt neoplastic masses. No neoplastic masses or cells were noted in the stained sections of liver or lymph node.
Photomicrographs of an excised portion of the pancreas of a 6-year-old Australian Shepherd that was evaluated at a veterinary referral center because of persistent hypoglycemia. A—The sizes of individual islets and overall islet area are subjectively large, with occasional coalescence of islets. H&E stain; bar = 100 μm. B—Ductuloinsular complexes comprising endocrine islets in intimate association with small-sized ducts. H&E stain; bar = 50 μm. C—Staining for pancytokeratin (clone AE1-AE3) accentuates exocrine ductular structures contiguous with a central islet. Immunohistochemical stain; bar = 50 μm. D—Staining for insulin shows strong cytoplasmic immunoreactivity by many presumptive β cells diffusely distributed within an islet. Immunohistochemical stain; bar = 50 μm. E—Staining for glucagon shows strong cytoplasmic immunoreactivity by a small number of presumptive β cells peripherally distributed within an islet. Immunohistochemical stain; bar = 50 μm. F—Staining for somatostatin shows strong cytoplasmic immunoreactivity by a moderate number of presumptive β cells extensively distributed within an islet. Immunohistochemical stain; bar = 50 μm.
Citation: Journal of the American Veterinary Medical Association 253, 7; 10.2460/javma.253.7.893
The pancreatic islet size, islet area, and islet numbers were objectively compared with those of a pancreas from an adult dog that was not affected by endocrine or exocrine disease at the time of procurement. The polyline area measurement tool of a virtual microscopy systemh was used for these assessments. The overall islet area from the patient's pancreas was substantially larger than that for the single control sample (160,000 vs 38,600 μm2/10 hpf [ie, 400×]), as was the mean ± SEM area per islet (11,428 ± 2,604 vs 2,593 ± 653 μm2/10 hpf). The islet numbers in the patient's pancreas (14/10 hpf) were similar to those in the control pancreas (15/10 hpf).
Pancreatic ducts and ductules had normal results (no immunoreactivity) for pancytokeratin and CK7 (Figure 1). Immunohistochemically, most islet cells had strong positive results (staining) for insulin. Islets also contained low numbers of cells with immunoreactivity for glucagon, and low to moderate numbers of cells with immunoreactivity for somatostatin. A paraffin-embedded pancreatic tissue block was submitted for Bartonella spp PCR assay.b The results of this test showed no amplification of bacterial DNA.
On subsequent recheck examinations 1, 2, and 8 months after surgery, the patient had no clinical signs of illness, and BG concentrations were within the reference range (66, 91, and 86 mg/dL, respectively). Eight months after surgery, a CBC and serum biochemical assessment revealed no clinically relevant abnormalities, and the patient remained euglycemic and apparently healthy without additional treatment.
Discussion
The term nesidioblastosis was first used by Laidlaw1 to designate neoformation or neodifferentiation of endocrine cells in the ductal epithelium of the exocrine pancreas. Nesidioblastosis was first described in children with congenital hyperinsulinemic hypoglycemia. In human adults, hyperinsulinemic hypoglycemia is mainly caused by insulinomas. Other causes of hyperinsulinemic hypoglycemia are rare and usually attributable to adult-onset nesidioblastosis, which was first described in 1975.2 Although, to the authors' knowledge, < 100 cases have been reported since the late 1970's, the diagnosis of nesidioblastosis seems to be reported with increasing frequency. This may result from a generalized increase in awareness of the disease that has developed in conjunction with advancements in diagnostic imaging techniques and contrast-enhanced imaging.3 The cause of adult-onset nesidioblastosis is unknown, but there seems to be an association with gastric bypass surgery.4 Hypotheses regarding the mechanisms by which hypoglycemia arises following this surgical procedure range from β-cell expansion or altered β-cell function to non-β-cell factors such as low circulating concentrations of the appetite-stimulating and insulin counter-regulatory gastrointestinal hormone ghrelin, or alterations in other counter-regulatory hormones.4 Surgical intervention with partial pancreatectomy is recommended as a salvage procedure for definitive control of suspected nesidioblastosis in human patients that fail to respond to medical treatment (eg, diazoxide, somatostatin analogs, and glucocorticoids).5 The development of nesidioblastosis in animals has rarely been documented. Hyperplastic islets have been associated with senile pancreatic atrophy in rats and result, in part, from increased insulin demand in the face of declining islet cell function. In addition, proliferative changes in the islets of Langerhans may also occur in association with the spontaneous lobular or chronic relapsing pancreatitis that is found in certain strains of rats.6 A 2-day-old Simmental calf with arthrogryposis and astasia was reported to have pancreatic lesions associated with this disease; however, it is important to mention that this calf was normoglycemic and normoinsulinemic.7 A group of research Beagles was found to have incidental nesidioblastosis-like structural alterations of the pancreas on necropsy.8 However, all of the dogs examined had SG concentrations within the reference range, although circulating insulin concentrations were not measured, so it is unknown whether the pancreatic changes affected insulin-to-glucose concentration ratios.8
One clinical report9 described 2 young dogs with suspected hyperinsulinemic hypoglycemia syndrome and bartonellosis confirmed either by culture of a blood sample on Bartonella spp α-proteobacteria growth medium or PCR analysis of a tissue sample. Histologic examination of pancreatic tissue from these 2 dogs (euthanized because of persistent hypoglycemia despite treatment) was not consistent with nesidioblastosis.9 Considering the similar biochemical abnormalities in the dog of the present report, we submitted a sample of pancreatic tissue for Bartonella spp testing by PCR analysis, but results were negative. In some human patients, pancreatogenous hyperinsulinemic hypoglycemia has been attributed to morphological changes consistent with nesidioblastosis.10 It is unclear whether hyperinsulinism is entirely attributable to the described histologic changes, and results of 1 literature review11 revealed that nesidioblastosis was present at autopsy in 36% of patients who did not have a previous history of hypoglycemia. Some authors suggest that all of the histopathologic criteria used to define diffuse nesidioblastosis in adult patients are unclear or even questionable.12 Some have used the term nesidioblastosis to designate any proliferation of endocrine cells from the ductal epithelium of the pancreas.12 However, this diagnosis is frequently made in cases of nontumorous β-cell proliferation leading to persistent hyperinsulinemic hypoglycemia of infancy or noninsulinoma pancreatogenous hyperinsulinemic hypoglycemia in adults.12 Many authors are reluctant to use the term nesidioblastosis because it literally refers to islet cells budding off from ducts. Today, this histologic finding is considered to be highly suggestive of but not mandatory for the diagnosis of nesidioblastosis.10 It is clear that the definition of nesidioblastosis has undergone a refinement as human medical research has progressed. Nonetheless, 2 of the more commonly accepted pathological criteria for establishing this diagnosis are the presence of variably sized, enlarged islets (often with a somewhat irregular outline) and poorly defined endocrine cell clusters scattered in the acinar parenchyma and occasionally intimately connected with small or large ducts (ductuloinsular complexes).13 The histopathologic findings for the dog of this report were compatible with these criteria. In light of these findings and the lack of a neoplastic population in the examined pancreatic tissue, a diagnosis of nesidioblastosis appeared appropriate. Histochemical staining of the tissue with antibodies against insulin, glucagon, and somatostatin showed strong immunoreactivity in varying numbers of cells. A similar staining pattern was reported in dogs for which nesidioblastosis was noted as an incidental finding.14 On histologic evaluation, our patient had substantially larger overall pancreatic islet area and mean area per islet, compared with a pancreatic sample from a dog considered free of endocrine or exocrine disease; however, this should be interpreted cautiously as comparisons were made with only 1 dog. Finally, ACTH stimulation test results and endogenous plasma ACTH concentrations in the dog of this report were not consistent with hypoadrenocorticism. The ACTH stimulation values were initially lower than expected, most likely owing to a suspected relative adrenal insufficiency that is often appreciated in human and canine patients with critical and possibly chronic illnesses. Taken together, the results of the hematologic and histologic evaluations and the clinical signs in the dog of this report were consistent with nesidioblastosis, which can be focal or diffuse. In light of the response to surgery (remission following partial pancreatectomy), it was assumed that the altered islet cell changes were focal in nature and localized to the removed section of pancreas. To our knowledge, this is the first report of nesidioblastosis in a dog for which clinical signs and biochemical abnormalities resolved following partial pancreatectomy. Although extremely rare, nesidioblastosis should remain a differential diagnosis in canine patients with endogenous hyperinsulinemic hypoglycemia, particularly in patients without any detectable pancreatic tumor.
ABBREVIATIONS
| BG | Blood glucose |
| SG | Serum glucose |
Footnotes
Cortrosyn, Amphastar Pharmaceuticals Inc, Rancho Cucamonga, Calif.
IDEXX Laboratories, Worthington, Ohio.
Prednisone, West-Ward Pharmaceuticals Corp, Eatontown, NJ.
Tramadol, Amneal Pharmaceuticals, Hauppauge, NY.
Traumeel, MediNatura, Berwyn, Pa.
EnVision FLEX HRP, Dako, Carpinteria, Calif.
Biocare Medical, Pacheco, Calif.
Philips Image Management System 2.3, IMS 2.3, Koninklijke Philips NV, Amsterdam, Netherlands.
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